WO 2004/032523 A1 discloses a color display device which is provided with a plurality of picture elements. The display device has more than the usual three display primaries to be able to display a wider gamut of colors. Two selectable light sources have different predetermined radiance spectra. Color filters in combination with the selectable light sources are able to produce respective first and second primary colors on the display device. A controller selects alternatively one of the selectable light sources and provides a portion of the picture elements with image information corresponding to the respective primary colors obtainable with the selected light source. The primary colors of the display device can be selected in a time sequential and space sequential way which enables a reduction of the color break up.
In an embodiment, this spectral sequential display drives two sub-frames for each input frame defined by input pixel values. During one of the sub-frames the light source with a first spectrum produces light while the other light source is inactive, and during the other one of the sub-frames the light source with a second spectrum produces light while the light source with the first spectrum is off. There are n different color filters associated with n sub-pixels per pixel of the display device. The light produced by a particular pixel depends on which light source is active, which color filter is associated with the particular pixel and which drive value is supplied to the particular pixel. The drive value may control the transmission of the pixel.
This prior art shows in FIG. 17 a color gamut for a color display device which uses two sub-fields per field, wherein two light sources are present which are active sequentially, each one during one of the two sub-fields, and wherein two sub-pixels are illuminated per subfield. In the luminance-chrominance representation of FIG. 17, the primaries Pa, Pb represent the colors of the two sub-pixels illuminated by the first light source during the first subfield, and the primaries Pc, Pd represent the colors of the other two sub-pixels illuminated by the second light source during the second subfield. This gamut is further referred to as the full gamut.
FIG. 18 of the prior art shows a sub-gamut which can be achieved with equal luminance and equal chrominance in both spectra defined by on the one hand the primaries Pa and Pb and on the other hand the primaries Pc and Pd. The colors in this sub-gamut, which is further referred to as the equal luminance and equal chrominance sub-gamut, can be produced in the two subfields with equal luminance and equal chrominance.
FIG. 19 of the prior art shows a sub-gamut which can be achieved with equal luminance in both subfields. This sub-gamut, which is further referred to as the equal luminance sub-gamut, comprises the equal luminance and equal chrominance sub-gamut.
WO 2004/032523 A1 discloses an approach to reduce color break up in a sequential display. If the input color of an input pixel is within the equal luminance and equal chrominance sub-gamut, the drive values of the sub-pixels during the two successive subfields are selected to obtain an equal luminance and an equal chrominance during these two subfields. If the input color of an input pixel is outside the equal luminance and equal chrominance sub-gamut but within the equal luminance sub-gamut, the drive values of the sub-pixels during the two successive subfields are selected to obtain an equal luminance during these two subfields. Although this prior art provides a high performance, it does not disclose how to efficiently determine the drive values of the sub-pixels during the subfields.